Basecoat/clearcoat (pigmented coating overlaid with a clearcoat layer) finishes for vehicles, such as, automobiles and trucks, are currently being widely used. Typically, such finishes are produced by a wet-on-wet method. In the method for applying a basecoat/clear coat finish, a basecoat (commonly referred to as a color coat) containing color pigment and/or special effect imparting pigment, is applied and flash dried for a short period of time, but not cured. Then the clear coating composition, which provides protection for the color coat and improves the gloss, distinctness of image and overall appearance of the finish, is applied thereover and both the color coat and the clearcoat are cured together. Optionally, the basecoat can be dried and cured before application of the clear coat.
Scratching and marring of the clearcoat finish continues to be a problem for vehicle finishes, particularly, wet scratch and mar resistance of such finishes. Clearcoat finishes on automotive vehicles are often subjected to mechanical damage caused by a variety of events during normal use. For example, materials that come in contact with the clear coats under normal use on the roadways, such as stones, sand, metal objects and the like, cause chipping of the clear coat finish. Keys used to lock and unlock vehicle doors cause scratches of the finish. Automated car wash equipment and brushes cause marring and scratching of the clear coat finish. The placement of sliding objects on the surface of an automotive vehicle such as the top of a trunk or hood causes scratches and marring. Also, the clear coat finish is subject to environmental damage caused, for example, by acid rain and exposure to UV light.
Attempts have been made to solve these problems by the addition of finely divided hard materials, such as silica, to the clearcoating composition. However, such particles often cause the resulting finish to have a dull appearance and reduced transparency, which are unacceptable appearance properties for automobiles and trucks. In Campbell et al. U.S. Pat. No. 5,853,809, inorganic microparticles were incorporated into a coating composition using an agent that reacted with the microparticles and with the crosslinking agent which resulted in relatively uniform distribution of the microparticles in the final cured clear coat finish. However, this did not significantly improve scratch and mar resistance of the clear coat finish and in some cases significantly reduced the transparency of the finish.
In Anderson et al. U.S. Pat. Nos. 6,759,478 and 6,387,519, clear coating compositions were formed with inorganic microparticles, which resulted in clear coat finishes on curing that had a stratified layer of microparticles at or near the surface of the finish which improved scratch and mar resistance. However, when the stratified layer is worn through or penetrated by damage caused, for example, by automatic car washing or exposure to the elements, the scratch and mar resistance performance of the finish deteriorates significantly.
There is a need for a clear transparent vehicle finish that has enhanced scratch and mar resistance, particularly under wet conditions and that has an excellent appearance and good optical properties. Automobiles and trucks having a finish of this invention have an acceptable automotive quality appearance and are resistant to both mechanical abrasion under wet conditions and to degradation by exposure to the elements.